Yersinia pestis is a human pathogen that is the causative agent of plague. Unfortunately, due to the high mortality rates and severe disease caused by Y. pestis, Y. pestis has emerged as a potential agent of biological warfare and bioterrorism. Although environmental outbreaks of plague largely have been controlled through the use of modern public health measures, the potential use of this pathogen as an agent of warfare and terror necessitates a more detailed understanding of the pathogenesis of Y. pestis to facilitate the identification of targets for vaccine development and treatment. No vaccine is currently available for either the bubonic or pneumonic form of plague. Examination of the recently published genome of Y. pestis indicates that Y. pestis potentially could express six different autotransporter (AT) proteins (designated Yap for Yersinia autotransporter protein). AT proteins have been identified in a wide variety of pathogens and as their name suggests the primary sequence of the protein is sufficient to direct transport across the outer membrane of the bacterium. In addition, in cases where the function of the AT is known these proteins are uniformly associated with virulence. The presence of six such sequences in the Y. pestis genome is of interest from the standpoint of understanding the interaction of Y. pestis with its host as well as potential vaccine candidates. Thus, to begin to study these ATs of Y. pestis we propose the following specific aims: Aim 1. Analysis of expression and localization of the Yaps in Y. pestis. Six different Yaps are predicted from the genome sequence and they may not all be expressed at the same time or localized in the same manner. A better understanding of the conditions under which each of the yaps is expressed and localized will provide valuable clues as to its potential function. Aim 2. Analysis of the role of Yaps in the virulence of Y. pestis. Mutants of each of the yap genes will be constructed in the CO92 strain of Y. pestis and then tested for virulence using the mouse model of infection. Aim 3. Functional analysis of the Yaps. We will begin to investigate the function of the Yaps by testing E. coli expressing individual Yaps for a variety of known functions previously associated with autotransporter proteins.